NASA has announced an iPad app that shows the Earth changing before a user's eyes, with interactive before-and-after views of the planet's altered face.

The Images of Change iPad application will illustrate the impact of human activities, a changing climate and natural disasters on the Earth by presenting pairs or sets of images of places around the world that have changed dramatically, NASA reported Tuesday.

"Images of Change gives users an astronaut's or Earth explorer's view of the changes occurring on our planet and demonstrates the important role NASA plays in contributing to the long-term understanding of Earth," John Grunsfeld, NASA's associate administrator for science in Washington, said. "By utilizing ground-based and space-based observation systems, we are able to better understand how humans are contributing to a changing world."

The app's gallery includes satellite views as well as photos taken at ground level, NASA said, and users can view images side-by-side or overlay them using a slider bar to travel from past to present.

The Images of Change iPad app is available as a free download at: http://go.nasa.gov/1bE3osn.